FactCheck.org is a project of the Annenberg Public Policy Center of the University of Pennsylvania. Its mission is to “apply the best practices of both journalism and scholarship” to “reduce the level of deception and confusion in U.S. politics.”

FactCheck.org recently published an article entitled “Santorum’s science,” by Lori Robertson. In this piece, Robertson criticizes Rick Santorum for a statement he made about global warming on March 12th in Biloxi, Mississippi. Alluding to the fact that carbon dioxide (CO2) is a vital ingredient for plant life, Santorum quipped, “The dangers of carbon dioxide? Tell that to a plant, how dangerous carbon dioxide is.”

Robertson attempts to refute Santorum’s remark by declaring:

• “Too much” CO2 “is definitely a bad thing.”
• “Exposure to high levels of CO2 can cause ‘headaches, dizziness, restlessness … coma, asphyxia to convulsions … and even frostbite if exposed to dry ice,’ which is solid CO2.”
• “Plants do, in fact, absorb CO2. But even plants might not like too much of it. A 2008 study conducted at the University of Illinois found that instead of increasing organic matter in soil, higher carbon dioxide levels actually led to less organic matter.”

These statements are materially misleading. Let’s examine them one at a time.

FactCheck.org: “Too much” CO2 “is definitely a bad thing.”

The same can be said of just about every substance known to man. The most basic principle of toxicology is that “the dose makes the poison.” As explained in a Cambridge University Press textbook, Understanding Environmental Pollution (page 60), “Anything is toxic at a high enough dose. … Even water, drunk in very large quantities, may kill people by disrupting the osmotic balance in the body’s cells.”

Likewise, even oxygen can be toxic when breathed in high concentrations. Per The Johns Hopkins Manual of Gynecology and Obstetrics (page 40), “when there is too much oxygen … the lungs may be damaged, as in acute repository distress syndrome (ARDS).”

Thus, it is meaningless to proclaim that “too much” of any particular substance is “a bad thing.” Instead, the pertinent matter is, “When does it become a bad thing?” which leads directly to the next point.

FactCheck.org: “Exposure to high levels of CO2 can cause ‘headaches, dizziness, restlessness … coma, asphyxia to convulsions … and even frostbite if exposed to dry ice,’ which is solid CO2.”

This statement is irrelevant to the issue at hand. Santorum was speaking about global warming and atmospheric CO2—not ventilation deathtraps, industrial hazards, and dry ice. The truth is that atmospheric CO2 levels don’t approach anywhere near the doses that can cause the symptoms that Robertson lists.

Using data from multiple academic sources, Just Facts has documented that carbon dioxide produces no adverse physiological effects on humans until concentrations exceed 50 times the level in Earth’s atmosphere. Furthermore, natural emissions of CO2 outweigh man-made emissions by a factor of twenty to one.

Some of Robertson’s confusion may stem from the source that she cites for the dangers of CO2, which is a cut sheet from the Wisconsin Department of Health and Family Services. This document contains a major recurring error. The figures given for CO2 concentrations that cause various adverse effects are mistaken by more than a factor of ten.

For example, the cut sheet says that exposure to CO2 concentrations above 5,000 parts per million (ppm) “may lead to serious oxygen deprivation resulting in permanent brain damage, coma and even death.” As detailed by the National Research Council (and many other academic sources), humans can be routinely exposed to more than ten times this level of CO2 for days on end without any indications of permanent brain damage or threat of death. In fact, it takes prolonged CO2 exposures of more than 20,000 ppm just to cause occasional, mild headaches.

FactCheck.org: “Plants do, in fact, absorb CO2. But even plants might not like too much of it. A 2008 study conducted at the University of Illinois found that instead of increasing organic matter in soil, higher carbon dioxide levels actually led to less organic matter.”

First, according to the article that Robertson cites for this claim, this study found that higher CO2 levels “may” have led to less organic matter in the soil of a certain soybean crop. This is different from claiming that higher CO2 “actually” led to less organic matter in plant soil.

Far more significantly, Robertson fails to mention that the study found “a 30 percent increase in above- and below- ground soybean biomass” among the crops exposed to more CO2. In plain language, these soybean plants grew 30% larger. They did, in fact, “like” the added CO2.

Note that this study was conducted at a CO2 level of 550 ppm, as compared to the current atmospheric CO2 concentration of about 387 ppm. Bear those figures in mind, because the study’s result accords with an academic text that explains how to increase the productivity of commercial greenhouses:

Plants need water, light, warmth, nutrition and CO2 to grow. By increasing the CO2 level in the greenhouse atmosphere (typical to 600 ppm instead of normal 400 ppm value), the growth for some plants can be stimulated in an important way, with often yield increases up to 20%, especially for tomato, cucumber, strawberry, etc. but also for potted plants and cut flowers.